System and method for detecting flow in a mass flow controller

ABSTRACT

Systems and methods are provided for detecting flow in a mass flow controller (MFC). The position of a gate in the MFC is sensed or otherwise determined to monitor flow through the MFC and to immediately or nearly immediately detect a flow failure. In one embodiment of the present invention, a novel MFC is provided. The MFC includes an orifice, a mass flow control gate, an actuator and a gate position sensor. The actuator moves the control gate to control flow through the orifice. The gate position sensor determines the gate position and/or gate movement to monitor flow and immediately or nearly immediately detect a flow failure. According to one embodiment of the present invention, the gate position sensor includes a transmitter for transmitting a signal and a receiver for receiving the signal such that the receiver provides an indication of the position of the gate based on the signal received. Other embodiments of the gate position sensor are described herein, as well as systems and methods that incorporate the novel MFC within a semiconductor manufacturing process.

RELATED APPLICATION(S)

This application is a Divisional of U.S. application Ser. No. 10/674,963filed Sep. 29, 2003, which is a Divisional of U.S. application Ser. No.09/945,161 filed Aug. 30, 2001, now U.S. Pat. No. 6,627,465, both ofwhich are incorporated herein by reference.

TECHNICAL FIELD

This invention relates generally to the detection of flow and flowfailure in a mass flow controller, and more particularly to the deliveryof semiconductor process gas in semiconductor manufacturing processesand the monitoring thereof for flow and flow failure.

BACKGROUND

An integrated circuit is formed in and on a wafer in semiconductormanufacturing processes. Forming an integrated circuit on a waferinvolves a number of sub-steps such as thermal oxidation, masking,etching and doping. In the thermal oxidation sub-step, the wafers areexposed to ultra-pure oxygen under carefully controlled conditions toform a silicon dioxide film, for example, on the wafer surface. In themasking sub-step, a photoresist or light-sensitive film is applied tothe wafer, an intense light is projected through a mask to expose thephotoresist with the mask pattern, the exposed photoresist is removed,and the wafer is baked to harden the remaining photoresist pattern. Inthe etching sub-step, the wafer is exposed to a chemical solution or gasdischarge to etch away or remove areas not covered by the hardenedphotoresist. In the doping sub-step, atoms with either one less or onemore electron than silicon are introduced into the area exposed by theetching process to alter the electrical character of the silicon. Thesesub-steps are repeated for each layer. Most of or all of these processesrequire the controlled introduction of gases into a processing chamber,and mass flow controllers are used to control the same. Each chip on thewafer is finally tested after the remaining metals, films and layershave been deposited. Subsequently, the wafer is sliced into individualchips that are assembled into packages.

Semiconductor gases are used in the above-described manufacturingprocess, and include, but are not limited to gases which serve asprecursors, etchants and dopants. These gases are applied to thesemiconductor wafer in a processing chamber. Precursor gases provide asource of silicon atoms for the deposition of polycrystalline silicon,epitaxial silicon, silicon dioxide and silicon nitride film within thethermal oxidation step. Etchant gases provide fluorocarbons and otherfluorinated materials that react with silicon, silicon dioxide andsilicon nitride. Dopants provide a source of controllable impuritiesthat modify the local electrical properties or characteristics of thesemiconductor material. A reliable supply of high purity process gasesis required for advanced semiconductor manufacturing. As thesemiconductor industry moves to smaller feature sizes, a greater demandis placed on the control technologies to accurately and reliably deliverthe semiconductor process gases.

Mass Flow Controllers (MFCs) are placed in an inflow line to control thedelivery of the semiconductor process gas. Conventional MFCs have aniris-like restricted orifice for controlling flow, and deliver gas orother mass at a low velocity. This low velocity allows interferingfeedback in the MFC; i.e. the pressure differentials occurring in thechamber travel back upstream through the gas and perturb the deliveryvelocity of the gas. Therefore, a problem associated with conventionalMFCs is that they are dependent on the characteristics of the specificchamber into which the gas is being delivered, and require trial anderror methods to find the proper valve position for delivering a desiredflow of material into the chamber. An obvious drawback to this approachis that the experimentation is very time consuming.

Ultrasonic MFCs meter gas flowing through an orifice of a known size ata velocity higher than the speed of sound. The mass flow is controlledusing a gated orifice by oscillating a gate between an opened and closedposition with respect to the orifice. The amount of material deliveredinto the chamber is adjusted by adjusting the duty cycle of theoscillations; i.e. by adjusting the amount of time per oscillationperiod that the gate is opened rather than closed. Because pressuredifferentials can only travel through the gas at the speed of sound,pressure variations in the chamber do not travel upstream quickly enoughto perturb the ultrasonic delivery velocity. Thus, ultrasonic MFCs havefeed forward control as they are able to deliver exactly the desiredamount of material into the chamber without being affected by anyfeedback from the chamber. However, a problem associated with ultrasonicMFCs is that control gates regulating the precision flow may fail bybecoming stuck either in an opened position, a closed position, or insome position in between the opened and closed positions. And in thecase of the above-described process for manufacturing semiconductors,this failure may not be detected for a considerable amount of timecausing considerable losses in both processing time and resources.

Therefore, there is a need in the art to provide improved MFC whichovercomes these problems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a novel MFC and electronic system for delivering amass and for detecting a flow failure according to the teachings of thepresent invention.

FIG. 2 illustrates a current detector embodiment of a gate positionsensor used in the MFC of FIG. 1.

FIG. 3 illustrates a physical wave generator/receiver embodiment of agate position sensor used in the MFC of FIG. 1, and a direct detectionmethod of using the same.

FIG. 4 illustrates a physical wave generator/receiver embodiment of agate position sensor used in the MFC of FIG. 1, and a signalinterference detection method of using the same.

FIG. 5 illustrates an optical detector embodiment of a gate positionsensor used in the MFC of FIG. 1.

FIG. 6 illustrates an electromagnetic pulse detector embodiment of agate position sensor used in the MFC of FIG. 1.

DETAILED DESCRIPTION

In the following detailed description of the invention, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown, by way of illustration, specific embodiments in which theinvention may be practiced. In the drawings, like numerals describesubstantially similar components throughout the several views. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilizedand structural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention.

The term wafer, as used in the following description, includes anystructure having an exposed surface with which to form the integratedcircuit (IC) structure of the invention. The term wafer also includesdoped and undoped semiconductors, epitaxial semiconductor layerssupported by a base semiconductor or insulator, as well as othersemiconductor structures well known to one skilled in the art. The termconductor is understood to include semiconductors, and the terminsulator is defined to include any material that is less electricallyconductive than the materials referred to as conductors. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

Systems and methods are provided for detecting flow and flow failure ina MFC. These systems and methods are particularly useful in deliveringsemiconductor gas in a semiconductor manufacturing process using anultrasonic MFC. The mass flow through the MFC is monitored by sensing orotherwise determining the position and/or motion of the gate in anultrasonic MFC. Therefore, the system is able to immediately or nearlyimmediately detect a flow failure, and provide an indication of thesame, caused by a gate being stuck in an opened position, a closedposition, or a position in between the opened and closed positions.Given the relatively long time horizon for semiconductor manufacturingprocesses and the fact that the testing is conducted late in theprocess, significant losses of manufacturing time and material areavoided through the early detection of flow failure.

In one embodiment of the present invention, a novel MFC is provided. TheMFC includes an orifice, a mass flow control gate, an actuator and agate position sensor. The mass flow control gate controls flow throughthe orifice, and the actuator moves the gate to control flow through theorifice. The gate position sensor senses or otherwise determines thegate position to monitor flow and immediately or nearly immediatelydetect a flow failure caused by a stuck gate. The novel MFC may beincorporated into an electronic system such as a semiconductormanufacturing system.

In a further embodiment of the present invention, a novel method isprovided. The method comprises the steps of providing a mass flowcontroller in an ultrasonic mass flow line, oscillating a gate in themass flow controller at a desired frequency between an opened and closedposition, and monitoring gate movement. This method may be incorporatedinto a method for delivering a semiconductor gas in a semiconductormanufacturing process, and into a method for detecting a gas flowfailure in a semiconductor manufacturing process.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the art byreference to the following description of the invention and referenceddrawings or by practice of the invention. The aspects, advantages, andfeatures of the invention are realized and attained by means of theinstrumentalities, procedures, and combinations particularly pointed outin the appended claims.

According to the teachings of the present invention, a novelchoke-orifice or gated-orifice MFC capable of detecting flow and flowfailure in the MFC is described. The MFC uses an oscillating controlgate to control or otherwise regulate the delivery of an ultrasonic gasor other substance. A gate position sensor senses or otherwisedetermines the position and/or the motion of the control gate. Thus, thegate position sensor can detect a stuck gate and thus detect flowfailure in the MFC. The gate position sensor may also be used to monitorthe oscillations of the control gate, and the duty cycle thereof, tocontinuously monitor the flow through the MFC by verifying that thecontrol gate is operating as anticipated and desired.

The MFC is described below first with respect to a general electronicsystem, and then in particular with respect to a semiconductormanufacturing system. Subsequently, the MFC itself and the gate positionsensor of the MFC is described in detail. Finally, specific methodsutilizing the MFC of the present invention are provided.

An electronic delivery system 110 incorporating a mass flow controller112 is generally illustrated in FIG. 1. The system 110 generallycomprises a source 114, a flow controller 112 connected to the source114 through an inflow line 116, a sensor 118, a processor 120, and anoutflow line 122 connected to a chamber 124. The inflow line 116delivers the substance from the source 114 to mass flow controller 112,which in turn regulates the flow of the substance out through theoutflow line 122. This delivered substance may comprise any material.Therefore, the flow controller 112 is often referred to as a mass flowcontroller (MFC). The flow controller 112 may be referred to as a liquidflow controller (LFC) if a liquid substance is being delivered by thesystem 110, or even a gas flow controller (GFC) if a gas substance isbeing delivered. However, for the purposes of this application and theteaching contained herein, the terms MFC, LFC and GFC are deemedequivalent as they both deliver a substance.

The MFC 112 is positioned in the flow, and is adapted for controlling orregulating the flow out through the outflow line 122. An ultrasonic MFC112 passes a high velocity flow (higher than the speed of sound) throughan orifice 226, specifically through a gated orifice. As describedthroughout this specification and as shown in the Figures, the termorifice 226 is intended to cover not only the opening through which themass flows, but also the surrounding structure that forms or defines theopening and that contacts the gate when the gate 228 is closed. A gate228 and corresponding actuator 230 for moving the gate 228, as generallyillustrated in FIG. 2 and is also illustrated in FIGS. 3-6 using likenumbers, is operably positioned proximate to the orifice 226 such thatthe gate 228 may oscillate between a closed position in which the flowthrough the orifice 226 is prevented, and an opened position in whichthe flow through the orifice 226 is allowed. The actuator 230 oscillatesor shutters the gate 228 between the opened and closed positions toregulate the ultrasonic flow through the orifice 226. The amount ofsubstance that is delivered through the MFC 212 is therefore dependentupon the duty cycle of the gate 228, which corresponds to the relativeamount of time that the gate 228 is opened rather than closed for eachopened-to-closed-to-opened cycle.

Referring again to FIG. 1, the gate position sensor 118 senses, detectsor otherwise monitors the position of the gate 128. In one embodiment ofthe present invention, the gate position sensor 118 determines whetherthe gate 128 is in an opened position or is in a closed position. Inother embodiments, the sensor 118 is designed to determine whether thegate 128 is moving as expected so as to verify proper operation.Additionally, the gate position sensor 118 may be designed to accuratelydetect the position that the gate 128 is in between the opened andclosed positions.

The electronic system 110 includes the processor 120 that is interfacedwith the actuator 130 of the control gate 128 to control the duty cycleof the gate 128. That is, the processor sends a control signal tooscillate the control gate 128 for the purpose of regulating the flowthrough the MFC 112. The processor 120 further may be interfaced withthe gate position sensor 118, and thus is able to determine the positionand/or motion of the control gate 128. The processor 120 may includeappropriate software programs to provide a number of functions,including but not limited to, verifying that the desired position of thecontrol gate 128 corresponds with the actual position of the controlgate 128 as sensed by the gate position sensor 118, providing feedbackcontrol to adjust the duty cycle to obtain the desired flow, and warningoperators of flow failure. Alternatively, in lieu of sending anindication signal from the gate position sensor 118 to the processor120, the sensor 118 may provide an output to an audio or visual device,or may otherwise provide a signal to other control circuitry.

FIG. 1 illustrates the electronic system 110 as a semiconductormanufacturing system in which the inflow line 116 is connected to asemiconductor process gas source 114. For an ultrasonic MFC, the inflowline 16 provides an ultrasonic gas flow to the MFC 112. As indicatedabove, the MFC 112 regulates the ultrasonic gas flow by oscillating thecontrol gate 128 between closed and opened positions with respect to theorifice 126. The regulated or controlled gas flow is delivered to aprocessing chamber 124 in which various semiconductor processes areperformed on the wafer. These processes may include, for example,deposition, etching, and doping. Also as illustrated in FIG. 1, the MFC112 may include a pressure and temperature transducer 132 interfacedwith the processor 120 to monitor the characteristics of the gas andprovide appropriate feedback control to the control gate 128.

Generally, the gate position sensor 118 includes a transmitter 134 fortransmitting a signal 136 and a receiver 138 for receiving the signal140. The receiver 138 provides an indication of whether the control gate128 is in an opened position, a closed position, or is in anotherposition based on the signal 140 received. The receiver 138 may alsoprovide a signal that the control gate is moving, either in addition toor in place of the position signal. The processor 120, or other controlcircuitry, interprets the signal 140 received by the receiver 138 toprovide an immediate or nearly immediate warning if there has been aflow failure or if the control gate 128 has otherwise malfunctioned. Asis described in more detail below with respect to the detaileddescription of the MFC 112 and the gate position sensor 118, there are anumber of embodiments for the gate position sensor 118. The followingembodiments provide a non-exhaustive list of sensor 118 designs fordetermining the gate position and/or gate movement that fall within theteachings of the present invention for determining flow and flowfailure.

In one embodiment, as generally illustrated in FIG. 2 and will bediscussed in more detail below, the gate position sensor 218 may includea device 242 that applies an electrical potential across the orifice 226and the gate 228 in the MFC 212. The sensor 218 further may include acurrent detector 244 that is able to detect a current flow through ajunction formed when the orifice 226 contacts the gate 228 when the gate228 is closed, i.e. an orifice/gate junction. Thus, in this embodiment,the transmitter 134 shown in FIG. 1 is the device 242 for applyingelectric potential across the gate 228 and an orifice 226 in the MFC212, the signal 136 and 140 shown in FIG. 1 is electric current 246flowing through the orifice/gate junction formed when the gate 228 isclosed, and the receiver 138 shown in FIG. 1 is a current detector 244for detecting current flowing through the orifice/gate junction.

In another embodiment, as generally illustrated in FIGS. 3 and 4 usinglike numbers and will be discussed in more detail below, the gateposition sensor 318 may include a physical wave generator 348 and atleast one physical wave receiver 350. The physical wave generator 348generates a physical signal 352 in the MFC 312. The physical wavereceiver 350 detects the physical signal 352 propagating from thegenerator 348 through an orifice/gate junction formed when the gate 328is closed. Thus, in this embodiment, the transmitter 134 of FIG. 1 isthe physical wave generator 348, the signals 136 and 140 of FIG. 1 arethe physical signal 352 propagating through the orifice/gate junctionformed when the gate 328 is closed, and the receiver 138 of FIG. 1 isthe physical wave receiver 350 for detecting the physical signal 352propagating through the orifice/gate junction.

In another embodiment, as generally illustrated in FIG. 5 and will bediscussed in more detail below, the gate position sensor 518 includes alight source 556 and a light detector 558. The light source 556 ispositioned on a first side of an orifice 526 in the MFC 512, and thelight detector 558 is positioned on a second side of the orifice 526.The light source 556 and light detector 558 are positioned and arrangedso that, as the control gate 528 oscillates between an opened position aclosed position with respect to the orifice 526, a light signal 560received by the light detector 558 and transmitted by the light source556 will be interrupted such that the gate position can be determined bythe interrupted signal. In one embodiment, the light source 556 andlight detector 558 are placed on opposing inflow and outflow ends of theorifice 526. Thus, in this embodiment, the transmitter 134 of FIG. 1 isthe light source 556, the signals 136 and 140 of FIG. 1 are the lightsignal 560 transmitted by the light source 556, and the receiver 138 ofFIG. 1 is the light detector 558 operably positioned with respect to thelight source 556 and the orifice 526 such that movement of the control528 gate oscillating between an opened position and a closed positioninterrupts the light signal 560 from being received by the lightdetector 558.

In another embodiment, as generally illustrated in FIG. 6 and will bediscussed in more detail below, the gate position sensor 618 includes amagnet 662, a cooperating induction coil 664, and an electromagneticpulse detector 666. Movement of the control gate 628 generates amagnetically induced signal in the induction coil 664 detectable by theelectromagnetic pulse detector 666. Thus, in this embodiment, thetransmitter 134 of FIG. 1 is the magnet 662, the signals 136 and 140 ofFIG. 1 are magnetic flux 668 from the magnet 662, and the receiver 138of FIG. 1 is the combination of the cooperating induction coil 664 andthe electromagnetic pulse detector 666 for detecting a magneticallyinduced signal in the induction coil 664. The control gate 628 movementinduces the signal in the coil by providing relative movement betweenthe magnet 662 and the coil 664.

The MFC 112 of FIG. 1 is illustrated in more detail in FIG. 2 and inFIGS. 3-6 using like numbers. The illustrated MFC has a generallycylindrical structure 268, somewhat akin to the shape of a conventionalgas inflow line. However, the illustrated structure 268, and thearrangement of the elements within, is not intended to describe anyspecific MFC or MFC structure, but rather is intended solely for thepurpose of illustrating the present invention.

In addition to the structure 268, the MFC 12 generally comprises anorifice 226 defined herein to include the surrounding structure thatdefines an opening, a mass flow control gate 228, an actuator 230, and agate position sensor 218. The control gate 228 is movable toward andaway from the orifice 226 to control flow through the orifice 226. Inresponse to a control signal from the microprocessor 120, for example,the actuator 230 moves the control gate 228 as desired either toward theorifice 226 into a closed position or away from the orifice 226 into anopened position. In this manner, the actuator 230 oscillates the controlgate 228 through a desired duty cycle between a closed position and anopen position to control flow through the orifice 226. The duty cyclecontrols the flow, and is determined by the total time that the controlgate 228 is in an open position in comparison to the entire period oftime it takes to move the control gate 228 from an open position to aclosed position and back to the open position. The gate position sensor118 is adapted to determine the position and/or movement of the controlgate 228. And as illustrated above with respect to FIG. 1, the gateposition sensor 118 generally can be considered to include a transmitter134 for transmitting a signal 136 and a receiver 138 for receiving thesignal 140. The receiver 138 provides an indication of a gate positionor a gate movement based on the signal received. This indication may beprovided as an input to the processor 120, to other control circuitry,or to audio or visual indicators.

According to the teachings of the present invention as indicated aboveand as generally illustrated in FIG. 1, a gate position sensor 118 isused to sense or detect the position and/or the movement of the controlgate 128 of the MFC 112. The sensor 118 may either form part of the MFC112, or may be a separate component of an electronic system 110 thatcontains a MFC 112. Also according to the teachings of the presentinvention and as one skilled in the art would understand, the specificdesign of the gate position sensor 118 may vary. That is, the specifictransmitter 134 and receiver 138 that is selected, and the arrangementthereof, may vary according to the particular characteristics of theactual physical devices. Therefore, the following embodiments of thegate position sensor 118 is intended as a non-exhaustive list of sensordesigns that would enable one skilled in the art to design and build thesame or equivalent sensor.

Referring now to FIG. 2, the illustrated gate position sensor 218includes a device 242 for applying an electrical potential across theorifice 226 and the control gate 228. The device 242 may include, but isnot limited to, a battery or an electronic voltage supply. For example,it is anticipated that it may be desirable to use a switchable powerdevice as the device 242 for applying electric potential. Anorifice/gate junction is formed to complete a circuit when the controlgate 228 is closed. A current detector 244 is able to detect the currentflow 246, or an increase in current flow, through the orifice/gatejunction. Based on the detection of this current 246, the system 110 isable to determine that the control gate is closed 228. Any number ofcurrent detection means may be used to detect the current. Therefore,one skilled in the art would be able to design or provide an appropriatedetection circuit for a particular device. Electrical connections areillustrated at the arm of the gate 228 and at the orifice 226.Therefore, the gate 228 and orifice 226 form a conductor through whichcurrent may pass when the control gate 228 is closed and theorifice/gate junction is formed.

When the control gate 228 is open, no current other than leakagecurrents through alternative pathways within the entire structure 268will be detected. The MFC 212 may be designed such that adequateelectrical insulation is maintained for all alternative pathways so thatleakage current intensities will be orders of magnitude lower than theclosed orientation current. As the conductivity of the structure 268 andthe specific characteristics of the actuator 230 vary, it is anticipatedthat one skilled in the art would be able to determine thesecharacteristics and design an appropriate electrical circuit thatpermits the system to detect current through the orifice/gate junctionand otherwise operate as intended without causing any damage to theequipment.

Referring now to FIGS. 3-4, the gate position sensor 318 is illustratedto include a physical wave generator 348 for generating a physicalsignal 352 and at least one physical wave receiver 350 for receiving thephysical signal 352. As one skilled in the art would recognize based onthe teachings of the present invention, the positions of the generator348 and receiver 350 may vary. The receiver 350 may be considered to bea transducer that forms a vibration sensor or switch. The physical wavegenerator 348 and the physical wave receiver 350 may be formed usingpiezoelectric crystals. However, this embodiment of the invention is notso limited to the use of piezoelectric crystals.

The physical wave generator 348 is driven with an ultrasonic frequencyand sends ultrasonic physical waves through the structure 368. Thereceiver 350 receives the ultrasonic wave form 352 through theorifice/gate junction formed when the control gate 328 is closed. Whenthe control gate 328 is open, the wave energy can only be received bythe receiver 350 via a secondary pathway, i.e. physical signal 454 inFIG. 4 for example, throughout the structure 368, and therefore willregister as a much lower intensity or amplitude. The system 110 is ableto determine that the control gate 328 is in a closed position when thephysical signal receiver 350 provides an indication that it has detectedthe physical signal 352 which propagated through the gate/orificejunction.

A direct physical wave detection method is illustrated in FIG. 3;namely, the physical wave receiver 350 directly detects the closed gateby sensing an increased amplitude in the physical signal received by thereceiver 350 caused by the signal 352 being directly transmitted throughthe orifice/gate junction. When the control gate 328 is closed, thesignal detected by the receiver 350 will be strong due to the directconnection between the generator 348 and the receiver 350. When thecontrol gate 328 is open, the signal will be weak due to a non-existentor weak signal 354 being transmitted elsewhere throughout the structure368, depending on the physical construction of the system. In otherwords, a portion of the generated physical wave may be transmitted assignal 454 of FIG. 4 throughout the structure and as signal 352 throughthe orifice/gate junction. The received physical signal will besignificantly higher if a direct signal path 352 is provided between thephysical wave generator 348 and physical wave receiver 350.

A physical wave signal interference detection method is illustrated inFIG. 4; namely, the physical wave receiver 450 is adapted for detectingand distinguishing a complex wave formed from a superposition of a firstphysical signal 454 and a second physical signal 452. It simplifies thisanalysis to consider that the structure 468 has at least two separatepathways 452 and 454 for the physical wave transmission to be detectedat the receiver 450. The required time for each transmission is afunction of the entire structure 468, and the interferences between thesignals 452 and 454 from all possible paths will give a complex waveformat the receiver 450. The first physical signal 454 is propagatedthroughout the structure 468 when the control gate 428 is open. For agiven generator 448/receiver 450 arrangement on a given structure 468,the first physical signal 454 will have a signature wave form. Thesecond physical signal 452 is directly propagated from the physical wavegenerator 448 to the physical wave receiver 450 through the orifice/gatejunction formed when the control gate 428 is closed. Similarly, for agiven generator 448/receiver 450 arrangement on a given structure 468,the second physical signal will have a signature wave form. It followsthat the superposition of the first and second signals 454 and 452 willalso have a signature wave form. These signature waveforms arerepeatable. Therefore, for physical wave signal interference detectionmethod, the system 110 includes circuitry capable of distinguishing thefirst signal 454 from the superposition of the first and second signals454 and 452 in order to determine whether the control gate 428 isclosed.

Alternatively, other receivers/transducers could be located atintermediate positions between the generator 348 and the receiver 350.The generator 348 may send a coded signal, and the arrival time of thecoded signal at each receiver/transducer would indicate whether thecontrol gate 328 is opened or closed.

As another alternative, the physical wave generator may be considered tobe the control gate 328 itself as it produces a physical wave throughoutthe structure 368 each time it closes. In this situation, the physicalwave receiver 350 is positioned and arranged to detect, and if necessarydistinguish from other physical signals, the physical signal generatedby the gate 328 when it closes. This embodiment monitors theself-generated sound wave of a gated orifice.

Referring now to FIG. 5, the gate position sensor 518 is illustrated toinclude a light source 556 positioned on a first side of the orifice 526and a light detector 558 positioned on a second side of the orifice 526.Movement of the control gate 528 oscillating between an opened positionand a closed position interrupts the light signal 560 from beingreceived by the light detector 558. As one of ordinary skill wouldunderstand from reading this disclosure, there are a number of possiblelayouts of the light source 556 and the light detector 558 that could beused to detect a gate position or gate motion. One, as illustrated inFIG. 5, shows the light source 556 and the light detector 558 onopposing inflow and outflow ends of the orifice 526 such that the lightdetector 558 receives the light signal 560 from the light source 556through the orifice 526. Another possible arrangement is to have thelight source 556 and the light detector 558 across the control gate 528from each other. A light detector 558 with a fast response will be ableto directly monitor the frequency of the opening and closing of the gate528, and thus give a direct measure of the gas flow through the MFC 512in addition to simply detecting whether the gate 528 is opened, isclosed, or is moving between the opened and closed positions.Additionally, the detection circuitry may be such as to detect thechange in intensity of the detected light signal 560 in order to detectthe position of a partially closed or partially opened gate 528.

Referring now to FIG. 6, the gate position sensor 618 is illustrated toinclude a magnet 662, a cooperating induction coil 664, and anelectromagnetic pulse detector 666. Movement of the gate 628 generates amagnetically induced signal in an induction coil 664 detectable by theelectromagnetic pulse detector 666. As one skilled in the art wouldunderstand from reading this disclosure, there are an number of designsthat may be used within this embodiment that still falls within theteaching of this invention. The magnet 662 may either be a permanentmagnet, as illustrated, or an electrically activated magnetic coil.Either the magnet 662 or the induction coil 664 may be attached to themoving arm of the gate 628, with the other operably located nearby sothat the changing magnetic flux 668 caused by the motion of the controlgate 628 will induce an electromagnetic signal in the induction coil664.

The Figures presented and described in detail above are similarly usefulin describing the method embodiments for operating MFCs, systemsincorporating MFCs, and gate position sensors incorporated in MFCs.

Therefore, according to the teachings of the present invention, a methodis taught comprising providing a mass flow controller in an ultrasonicmass flow line, oscillating a gate in the mass flow controller at adesired frequency between an opened position and a closed position toregulate the mass flow, and monitoring gate movement. In one embodiment,monitoring gate movement may include verifying an actual gate positionagainst a desired gate position, and/or transmitting a signal in themass flow controller, receiving the signal, and determining whether thegate is opened or closed based on the signal received. Additionally,oscillating a gate at a desired frequency may include varying a dutycycle to adjust mass flow through the mass flow controller.

Furthermore, according to the teachings of the present invention, amethod for delivering a semiconductor gas for a semiconductormanufacturing process is taught, comprising providing a mass flowcontroller in an ultrasonic semiconductor gas flow line, oscillating agate in the mass flow controller between an opened position and a closedposition, and monitoring operation of the gate by transmitting a signal,receiving the signal, and determining whether the gate is opened orclosed based on the signal received.

In one embodiment, transmitting a signal may include applying electricpotential across the gate and an orifice in the flow controller, andreceiving the signal may include detecting current flowing through anorifice/gate junction formed when the gate is closed.

In another embodiment, transmitting a signal may include generating aphysical wave in the mass flow controller using a physical wavegenerator, receiving the signal may include receiving a physical wave inthe mass flow controller using a physical wave receiver, and determiningwhether the gate is opened or closed may include determining whether atleast a component of the received physical wave was propagated throughan orifice/gate junction formed when the gate is closed.

In another embodiment, transmitting a signal may include transmitting alight signal in the mass flow controller, receiving a signal may includereceiving the light signal, and determining whether the gate is openedor closed may include determining whether the light signal is received.

In another embodiment, transmitting a signal may include producingmagnetic flux, receiving a signal may include detecting a magneticallyinduced signal in a cooperating induction coil positioned within themagnetic flux, and determining whether the gate is opened or closed mayinclude determining that the gate has moved if a magnetically inducedsignal is detected in the induction coil.

Additionally, according to the teachings of the present invention, amethod for detecting a gas flow failure in a semiconductor manufacturingprocess is taught, comprising providing a flow controller in asemiconductor gas inflow line, oscillating a gate in the flow controllerto control flow, and monitoring the gate to detect flow failure. In oneembodiment, monitoring the gate may include verifying an actual gateposition against a desired gate position. In another embodiment,monitoring the gate may include transmitting a signal, receiving thesignal, and determining whether the gate has moved or is moving based onthe signal received. In another embodiment, monitoring the gate mayinclude determining that the gate is either stuck in an open position orstuck in a closed position.

Thus, the present invention provides novel systems and methods fordetecting flow and flow failure in a mass flow controller. These systemsand methods are particularly useful as used within semiconductormanufacturing processes. The invention is not limited to theseprocesses, however. The novel mass fluid controller (MFC) of the presentinvention provides an ultrasonic delivery using a gated orifice, andfurther provides a gate position sensor for detecting flow and flowfailure in the MFC. Unlike conventional MFCs, the ultrasonic MFC of thepresent invention has feed forward control, and is not susceptible tofeedback interference caused by pressure differentials in the chamber.As such, the ultrasonic MFC provides an accurate delivery of asubstance. The ultrasonic MFC has an oscillating gate that moves betweenan opened position and a closed position to regulate or control flowthrough the MFC. Additionally, the ultrasonic MFC of the presentinvention includes a gate position sensor that senses or otherwisedetects the position and/or movement of the oscillating gate. As such,the gate position sensor determines if the gate is stuck or hasotherwise failed without notice, and thus guards against theconsiderable loss of process time and material that would likely occurwithout an immediate or nearly immediate detection and indication of aflow failure.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. It is to be understood that the above description is intendedto be illustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the inventionincludes any other applications in which the above structures andfabrication methods are used. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1. A gate position sensor, comprising: a transmitter for transmitting asignal in a flow controller, wherein a position of a gate in the flowcontroller affects the signal; and a receiver for receiving the signal,wherein the receiver is adapted to provide a signal output for thesensor to indicate a gate position within the flow controller based onthe signal received, wherein the transmitter is a physical wavegenerator, the signal is a physical wave propagating through a junctionformed by the orifice and the gate when the gate is closed, and thereceiver is a physical wave receiver for detecting the physical wavepropagating through the junction.
 2. The gate position sensor of claim1, wherein the receiver detects when the gate is in a closed position bysensing an increased amplitude in the physical signal received by thereceiver.
 3. The gate position sensor of claim 1, wherein the physicalwave receiver detects a complex wave formed from a superposition of afirst physical signal propagated through a structure when the gate is inan opened positioned and a second physical signal directly propagatedfrom the physical wave generator to the physical wave receiver when thegate is in a closed position.
 4. The gate position sensor of claim 1,wherein the physical wave generator and the physical wave receiverinclude piezoelectric crystals.
 5. The gate position sensor of claim 1,wherein the physical wave generator is the gate such that closing thegate generates a physical wave detectable by the physical wave receiver.6. The gate position sensor of claim 1, further comprising at least oneintermediate receiver located between the generator and the receiver. 7.The gate position sensor of claim 6, wherein the generator is adapted tosend a coded signal.
 8. A gate position sensor for a flow controllerhaving an orifice and a gate for closing the orifice, comprising: aphysical wave generator for generating a physical signal in the flowcontroller; and at least one physical wave receiver for detecting thephysical signal propagating from the generator based on a relativeposition of the gate to the orifice.
 9. The gate position sensor ofclaim 8, wherein the receiver detects when the gate is in a closedposition by sensing an increased amplitude in the physical signalreceived by the receiver.
 10. The gate position sensor of claim 8,wherein the physical wave receiver detects a complex wave formed from asuperposition of a first physical signal propagated through a structurewhen the gate is in an opened positioned and a second physical signaldirectly propagated from the physical wave generator to the physicalwave receiver when the gate is in a closed position.
 11. The gateposition sensor of claim 8, wherein the physical wave generator and thephysical wave receiver include piezoelectric crystals.
 12. The gateposition sensor of claim 8, wherein the physical wave generator is thegate such that closing the gate generates a physical wave detectable bythe physical wave receiver.
 13. The gate position sensor of claim 8,wherein the at least one receiver includes a first receiver and a secondreceiver intermediately positioned with respect to the first receiverand the generator.
 14. A system, comprising: an ultrasonic mass flowcontroller including a gate adapted to move between an open and closedposition; a sensor, including: a physical wave generator for generatinga physical signal in the flow controller; and at least one physical wavereceiver for detecting the physical signal propagating from thegenerator based on a relative position of the gate to the orifice. 15.The system of claim 14, wherein the at least one receiver includes afirst receiver and a second receiver intermediately positioned withrespect to the first receiver and the generator.
 16. The system of claim14, wherein the generator generates a coded signal.
 17. A system,comprising: an inflow line; a flow controller positioned in the inflowline for controlling flow, the flow controller including a gate and anactuator for moving the gate to control flow; a gate position sensor formonitoring whether the gate is in an opened position or a closedposition, the sensor including means for transmitting a signal in theflow controller such that a position of the gate in the flow controlleraffects the signal, and means for receiving the signal and providing asignal output for the sensor to indicate a gate position within the flowcontroller based on the signal received; and a processor for controllingthe position of the gate and for interfacing with the sensor, whereinthe sensor includes a physical wave generator and a physical wavereceiver, and wherein the physical wave generator generates a physicalsignal, at least one physical wave receiver receives the physicalsignal, and the physical wave receiver detects the physical signalpropagating from the generator through a junction formed by the orificeand the gate when the gate is closed.
 18. The system of claim 17,further comprising: a semiconductor gas source; and a semiconductorprocessing chamber, wherein the flow controller is adapted to controlgas flow through the inflow line from the gas source to the processingchamber.
 19. The system of claim 18, wherein the flow controllerincludes an ultrasonic mass flow controller.
 20. The system of claim 17,wherein the receiver detects when the gate is in a closed position bysensing an increased amplitude in the physical signal received by thereceiver.
 21. The system of claim 17, wherein the physical wave receiverdetects a complex wave formed from a superposition of a first physicalsignal propagated through a structure when the gate is in an openedpositioned and a second physical signal directly propagated from thephysical wave generator to the physical wave receiver when the gate isin a closed position.
 22. The system of claim 17, wherein the physicalwave generator and the physical wave receiver include piezoelectriccrystals.
 23. The system of claim 17, wherein the physical wavegenerator is the gate such that closing the gate generates a physicalwave detectable by the physical wave receiver.
 24. The system of claim17, further comprising at least one intermediate receiver locatedbetween the generator and the receiver.
 25. The system of claim 17,wherein the generator is adapted to send a coded signal.